High-vacuum plants



May 7, 1963 T. (JOSEF) KRAUS 3 0 219 HIGH-VACUUM PLANTS Filed April 7,1960 2 Sheets-Sheet 1 H 5 774/100 44/8 (dasEF) Kmrus May 7, 1963 T.(JOSEF) KRAUS 3,088,219

HIGH-VACUUM PLANTS Filed April 7. 1960 2 Sheets-Sheet 2 28 g g m 25 H 432 be/l0w: 5 38 37 Bell Valve I fiwv-Q-viw f re /400 905 (40551 mmusUnited States Patent Mad stein Filed Apr. 7, 1960, Ser. No. 20,790Claims priority, application Switzerland Apr. 7, 1959 7 Claims. or.34-15 The present invention relates to a high vacuum plant comprising arecipient having an access aperture to be opened for the insertion ofthe articles to be treated in vacuo and for the withdrawal of saidarticles after treatment.

The invention has the main object of providing a high vacuum plant ofthe kind referred to and a method of its operation capable ofsubstantially reducing the pumping time required for evacuating saidrecipient after the same has been opened for the insertion or withdrawalof the articles treated therein, and more particularly for shorteningthe pumping time for establishing a high vacuum after a previouspart-evacuation to a preliminary vacuum.

It is another object of the invention to achieve the aforesaid saving inpumping time without the use of sluice devices as hitherto used forkeeping the recipient proper constantly under vacuum, even whileinserting and withdrawing the articles undergoing treatment.

The purpose of such devices is naturally to save pumping time: with manyprocesses the treatment of the articles in vacuo takes only a fractionof the time required for pumping. For example a thin reflexion-reducinglayer may be deposited on a lens from the vapor phase easily within aminute, while it takes at least half an hour or longer to reach the highvacuum required for the operation after preliminary evacuation byprevious pumping.

The aforesaid sluice devices, which accordingly serve for saving pumpingtime, are however costly in construction, and are at present notsufiiciently developed for many articles to be treated in vacuo, forexample for lenses, so as to find use in industrial production.Accordingly the use of high vacuum plants, the recipient of which can beopened for the insertion and the withdrawal of the articles to betreated, has been continued and the losses in time involved thereby havebeen accepted.

It has now been found that even in such plants quite a considerableproportion of the pumping time, namely up to 99% and even more, can besaved at least for the high vacuum evacuation, by operating according toa new method of operation forming the subject of the invention describedhereinafter.

With the objects as aforesaid and other objects in view, which willbecome apparent later from this specification and the accompanyingdrawings, I provide a method for the operation of a high vacuum plantcomprising the steps of opening the recipient, inserting the articles tobe treated in vacuo into the said recipient and introducingsimultaneously into same a flow of dried gas of a humidity below that ofthe surrounding space, closing said recipient, evacuating saidrecipient, carrying out the treatment of the articles in vacuo,re-opening said recipient while introducing simultaneously into the samea flow of said dried gas, and withdrawing the treated articles.

A high vacuum plant according to my present invention comprises incombination: a recipient having an access aperture, a closure membercapable of closing said aperture, evacuating means operatively connectedto said recipient, and at least one dry gas introducing orifice arrangedinside said recipient and directed towards said access aperture, saidorifice being connected to an exter- 3,088,219 Patented May 7., 1963 nalsource of dried gas while said closure member is open.

Although it has been known that water vapour constitutes a considerableproportion of the gases or vapours which have to be pumped ofi whenestablishing a high vacuum in a conventional recipient, whether made ofglass or of metal, it is nevertheless quite surprising that suchenormous savings in pumping time can be attained by the simple measurementioned.

For example it may be mentioned that a metal vacuum recipient having acapacity of about litres required a regular high vacuum pumping time of88 minutes with existing pumps, in order to reach a vacuum of 4 l0- mm.Hg after preliminary evacuation to 10' mm. Hg. When however proceedingby the method according to the present invention, i.e. when constantlyblowing a gas sharply dried by phosphorus pentoxide into the recipient,

.while in the opened condition in communication with the externalatmosphere, then with the same pumps and without any other provisionsfor the high vacuum pumping (after a preliminary evacuation), pumpingtimes were attained amounting to fractions of a minute, for example of50 seconds for the range from 10- mm. Hg to 2X10- mm. Hg. Theseobservations have been confirmed on numerous other plants. It should beremarked that these achievements were attained not only in cases whenthe air of the external atmosphere was extraordinarilymoist, but quitegenerally, i.e. with the air of the external atmosphere having arelative humidity, lying between 20 and 60% of saturation.

It is obvious that the new method constitutes a big jump forward in thetechnical progress. Its application is recommended everywhere, wherearticles giving off comparatively little gas, such as glass or metalcomponents, are to be treated for short periods of time under a highvacuum, and subsequently the plant has at once to be charged anew. Inthese cases of application the efliciency and availability of anexisting high vacuum plant is enormously improved by the new method.

For carrying out the new method the following indications may be useful:

The blowing in of the dry gas is conveniently effected from a point inthe interior of the recipient in the direction towards the aperture,through which the recipient in the opened condition is in communicationwith the external atmosphere. It appears that thereby the ingress ofmoist ambient air is prevented more effectively. In order to makesavings in the rinsing gas blown into the recipient it is advisable tothrottle the outflow into the surrounding atmosphere by obstaclesarranged outside of the aperture of the recipient. Such obstacles whichcan be readily provided as a make-shift arrangement on existing plantsmay be constituted e.g. by curtains, which close the means of access tothe recipient from all sides except for small slots serving for theinsertion, the withdrawal and other manipulations required when therecipient is opened.

As regards the kind of the dry gas to be blown in, the following has tobe stated: in principle naturally all sufiiciently dry gases may beutilised insofar as they are chemically compatible with the articles tobe treated and with the components of the plant. It suifices, to usepreviously dried air. Dry CO has the advantage that it is readilycompressible so that even large quantities require only relativelysmall, handy containers for storage.

The choice of the rinsing gas is often determined by the technologicalprocess being performed. For example dry 0 may be blown into plantswherein oxidizing processes are to be carried out. In other plants, dryN argon or other known inert gases will be used. The use of an inert gasfor the protection of articles treated, for example in furnaces, isknown in itself, but for protecting the articles from high temperaturesor from chem ical activity, while the use of such gases in the driedstate for the purpose of shortening the evacuation periods has beenproposed for the first time by the'present invention.

The method according to the invention may also be carried out in severalstages, i.e'. the recipient may be surrounded'by an outer shell, and theatmosphere in the enclosed-space may be kept at a lower humidity thanthat corresponding to the external atmosphere. This may be done in thatthe enclosed-space is supplied with dry gas .(e.g. by constantly blowingin dry air), or by setting up conventional drying agents therein or bybuilding-in .a drying apparatus. Drying agents and drying apparatus maynaturally also be arranged in the recipient proper, if desired.

When calling the aforesaid enclosed space the 1st enclosed space, onecould say that the method according to the invention may be carried outby surrounding the recipient with a 1st, 2nd, etc. enclosed space, andby supplying all or some of said enclosed spaces with dry gas while therecipient is in the opened state. In the simplest case, the dry gas,which is blown into the recipient proper, is made to flow through theconsecutive enclosed spaces in succession.

These and other features of my said invention will be clearly understoodfrom the following description of some embodiments of my new andimproved vacuum plant given by way of example and not of limitation withreference to the accompanying diagrammatic drawings, in which:

FIGURE 1 is a diagrammatic longitudinal part section of a firstembodiment of a vacuum recipient with a device for blowing a dried gasinto the surrounding enclosed space;

FIGURE 2 is a diagrammatic representation on a smaller scale of a firstmodification; and

FIGURE 3 of a second modification of the embodiment according to FIGURE1, also on a smaller scale than FIGURE 1;

FIGURE 4 is a diagrammatic representation of another embodiment.

In FIGURE 1 the vacuum recipient 1 is formed by the bell 2 and theplatform 3. This recipient 1 can be evacuated through the pipe 4 bymeans of a pump 5. 6 denotes an annular seal, 7 denotes a hydraulichoisting device, by means of which the bell 2 can be raised and therecipient can be opened. The position of the raised bell is indicated inthis figure in dotted lines.

The recipient described, which rests on a base 8, is totally enclosed ina casing 9, which may be formed either of rigid walls or of a gas-tightsynthetic plastic material, e.g. a thin sheet of synthetic material. Thecasing 9 is connected in a gas-tight manner, to the base 8 by means ofthe flange 10 with annular seal 11, buthas one or several flaps ormovable resilient sleeves 13, through which articles can be insertedinto the recipient 1 (when the same is opened) or any othermanipulations can be carried out. When for example the recipientcontains a device for the deposition from the vapor phase of thin layerson lenses, the lenses may be introduced by hand through the sleeve 13.

FIGURE 1 moreover shows a blower 14 for aspirating atmospheric air, adrying device 15 for this aspirated air adjoining downstream of theblower and a pipe 16 leading into the interior 17 of the casing 9.Moreover a valve 18 is provided on the bell 2, through which air can belet into the recipient from the interspace between the casing 9 and thebell 2.

The device described can be used in the following manner according tothe method of the invention:

Firstly the hell 2 is assumed to be raised and the recipient to becharged with the articles to be treated in vacuo. Then the bell 2 isclosed, evacuated through the components 4 and 5, until the workingvacuum is attained,

and subsequently the vacuum treatment is carried out. During this perioda flow of dry air is continuously blown into the enclosed space betweenthe casing 9 and the outside of the bell 2. By the excess pressure whichconsequently prevails in this enclosed space the casing 9 is then keptin shape even when it consists of a thin sheet; moreover the sleeve 13is pressed against the wall of'the casing so that it is kept closed. Themovable flap 12 and collapsible sleeve 13 thus form obstacles againstthe outflow of dried air. The air introduced into said enclosed spacecan accordingly flow off to the external atmosphere only through theexisting small leaks, so that the consump tion of dry air remains low.The air flowing past the walls of the enclosed space carries along themoisture that would normally adhere to the outside of the bell 2 and tothe inside of the casing 9 in the form of an extremely thin film, sothat in the course of this operation these walls are practicallycompletely dried. This is, as explained hereinabove, of decisiveimportance for the shortening of the pumping time. a

After the vacuum treatment in the recipient has been terminated therecipient has to be opened in order to be able to take out the articlestreated, and to introduce new ones. For this purpose firstly the valve-18 is opened, so that the dry air from the enclosed space 17 flows intothe recipient. Thereafter the bell 2 is raised, the articles are takenout of the bell 2 and casing '9 through the flap 12 or sleeve 13, andany other manipulations which may become necessary, such as the exchangeof evaporation sources or the like, are carried out in the recipient.During this stage dry air constantly flows from the pipe 16 into thespaces 1 and 17, and flows oil? outward through the flap 12 andservicing sleeve 13, which are temporarily opened during themanipulations described. Any penetration of moist air from the externalatmosphere and accordingly any condensation on the walls of the bell andcasing are prevented by the flow of dry air or gas from pipe v16.

After the recipient has been made ready for renewed evacuation, the bell.2 is lowered, valve 18 is closed again, and the recipient 1 isevacuated through the pipe 4 by the pump 5. In this second and anyfurther evacuation the advantage of the method according to theinvention makes itself noted by substantially shortened pumping periods.Any further evacuation cycle is carried out in a similar manner asdescribed; it is essential that the moist air is kept away from theinner wall surface of the recipient and the apparatus componentscontained therein as well as from those parts outside thereof which arein gas interchange with the inner wall surface when the recipient isopened. It has been found that for example even cm. of an area which hadbeen in contact for a prolonged period with the external atmosphere(relative humidity about 50%) and then came into communication with therecipient, might prolong the pumping period by about 10 to 20 minutes.For this reason it is advisable previously to dry even the articles tobe treated before their insertion into the recipient. .For exampleduring the vacuum treatment of one charge, the articles to be treated inthe next consecutive charge may be deposited already in the enclosedspace 17 so that they are previously dried there in the air'current. Inorder to attain a uniform flow through the enclosed space 17, the tip 19of the casing 9 may have a restricted vent through which air can escapeoutward.

.Modified embodiments for carrying out the method according to theinvention are diagrammatically illustrated in FIGURES 2 to 4. In FIGURES2 and 3, respectively, 21 and 2-1 denote the recipient, 22 and 22' acasing surrounding the recipient, and 23 and 23' a cflap, sleeve orsimilar means of access for the same purpose. 24 and 124' denote theevacuating line, 25 and 25' the vacuum pump, and 26 and 26 a line, whichis in communication with a source 27 and 27' of dried gas. This sourcemay be a drying appliance (like of FIGURE 1) or for example a pressuregas container for extremely dry oxygen, nitrogen or any other suitablegas.

The embodiments according to the FIGURES 2 and 3 difler from that ofFIGURE 1 primarily in that the introduction of the dry gas into therecipient 21 or 21 and into the casing 22 and 22, respectively, takesplace partly at difierent points.

In FIGURE 2 the line 26 is directly connected with the recipient 21through a valve 28. In this arrangement dry air flows through theenclosed space 2.9 only when the recipient 21 is opened. While the sameis closed, the atmosphere in the enclosed space 29 is at rest; ifdesired, however, a fan may be used for circulating the air therein,which is convenient when in this enclosed space 29 a drying appliancecharged for example with phosphorous pentoxide is set up. In theembodiment according to FIGURE 2 the casing 22 (particularly its meansof access 23) should be capable of being closed so tightly that noappreciable quantity of the external air can penetrate into it duringthe treatment period. During the charging and discharging of this plantthe danger of penetration of moist air through the means of access 23 isobviated by the outward flow of dry gas through it.

In FIGURE 3 additionally a line provided with a valve 39 is arranged. Inthis arrangement dry air may be introduced simultaneously into therecipient 2.1 and into the enclosed space 29'. This construction isrecommended particularly for large plants; the operation is otherwiseanalogous to that described hereinabove with reference to the FIGURES 1and 2.

In FIGURE 4 a design is illustrated in which part only of the outside ofthe wall of the recipient is protected from the moist atmosphere. 31denotes a bell forming the recipient, 32 a vertical closure wall of thisbell, 33 the evacuation line, 34 the vacuum pump, 35 a rail on which thebell 31 is suspended by means of rollers 36 and can be movedhorizontally away from the wall 32 in order to open the recipient. Thebell 31 is here not fully enclosed by a casing (such as 9, 22, 22 in theother figures), but only over a short stretch at the left hand sidemargin of the bell 31. This envelope has here the form of an expansiblefolded bellows 37, which is attached on the one hand to the closure wall32 (along a circle 38) and on the other hand to the bell 31 (along acircumference 39). When the recipient is to be opened, it is driven awayfrom the wall 32 to the right, while the bellows 37 is stretched. At thesame time dry gas is introduced into the recipient through a valve 40,so that it flows through the same and escapes through the means ofaccess 41 into the bellows 37, thus preventing the moist external airfrom penetrating into the recipient. One of these means of access 41 isindicated in FIGURE 4 as a flap. When the charging is terminated, thebell is closed again. The bellows folds up and forms a small enclosedspace around the annular seal 42 between the bell 31 and the wall 32,which space remains filled with dry air and accordingly preventscondensation on the outside of the said seal and of the flange of thebell. Obviously, analogous to FIGURE 3, a separate supply line of drygas could be provided for this enclosed space in order to make even moresure that no moist air can penetrate into it.

While I have described herein and illustrated in the accompanyingdrawings what may be considered typical and particularly usefulembodiments of my said invention, I wish it to be understood that I donot limit myself to the particular details and dimensions described andillustrated; for obvious modifications will occur to a person skilled inthe art.

What I claim as my invention and desire to secure by Letters Patent, is:

l. A method for the operation of a high vacuum plant having anevacuatable recipient comprising the steps of opening the recipient,inserting dry articles to be treated in vacuo into said recipient andintroducing simultaneously into the same a flow of dried gas of ahumidity below that of the surrounding atmosphere, closing saidrecipient, evacuating said recipient to a pressure of the order below10* mm. Hg, carrying out the treatment of the articles in vacuo,re-opening said recipient while introducing simultaneously into the samea flow of the said dried gas from a point in the interior of saidrecipient towards the opening thereof, and Withdrawing the treatedarticles.

2. A method as claimed in claim 1, comprising the additional step ofmaintaining in the space surrounding said recipient an atmosphere of ahumidity 'lower than that of the ambient air.

3. A method for the shortening of the pumping time in discontinuouslyoperating vacuum plants having a vacuum recipient repeatedly to beopened and subsequently closed for inserting dry articles to be treatedtherein and for withdrawing the same after treatment, comprising theconsecutive steps of opening an access opening to said vacuum recipient,blowing dry gas of a humidity substantially lower than that of thesurrounding atmosphere from the interior of said vacuum recipientoutwardly in the direction towards said open access opening, closingsaid access opening, and evacuating said vacuum recipient to a pressureof the order below 10 mm. Hg.

4. A device for treating articles under high vacuum comprising incombination: a recipient, a casing surrounding said recipient at leastat one end thereof, means for moving said recipient from an open to aclosed position within said casing, a gas-tight sealing member engagedby said recipient in its closed position, means tor evacuating saidrecipient, means in said casing providing access to the interiorthereof, a flexible closure for said access means, a source of driedgas, and means for injecting said dried gas into the interior of saidcasing.

5. The device according to claim 4 including valved means for injectinga current of dried gas into the recipient.

6. The device according to claim 4 in which the gas injecting means islocated adjacent the access means in the casing.

7. The device according to claim 4 in which the flexible closure is aresilient sleeve.

References Cited in the file of this patent UNITED STATES PATENTS1,580,957 Chafle et al. Apr. 13, 1926 1,799,248 Reinhardt Apr. 7, 19311,866,346 Clark July 5, 1932 2,307,802 Reichel Jan. 12, 1943 2,465,963Beardslee Mar. 29, 1949 2,858,795 Walker Nov. 4, 1958 2,890,878Steinherz et al. June 16, 1959

4. A DEVICE FOR TREATING ARTICLES UNDER HIGH VACUUM COMPRISING INCOMBINATION: A RECIPIENT, A CASING SURROUNDING SAID RECIPIENT AT LEASTAT ONE END THEREOF, MEANS FOR MOVING SAID RECIPIENT FROM AN OPEN TO ACLOSED PORTION WITHIN SAID CASING, A GAS-TIGHT SEALING MEMBER ENGAGED BYSAID RECIPIENT IN ITS CLOSED POSITION, MEANS FOR EVACUATING SAIDRECIPIENT MEANS IN SAID CASING PROVIDING ACCESS TO THE INTERIOR THEREOF,A FLEXIBLE CLOSURE FOR SAID ACCESS MEANS, A SOURCE OF DRIED GAS, ANDMEANS FOR INJECTING SAID DRIED GAS INTO THE INTERIOR OF SAID CASING.